The present disclosure contemplates production of synthesis gas comprising CO, CO2, and H2 via gasification of carbonaceous materials. Synthesis gas can be used to produce one or more chemicals through biological or chemical routes. Synthesis gas can also be used to produce energy to generate electricity.
Thus syngas can be acted upon by fermentation or digestion by certain microorganisms to produce alcohols (methanol, ethanol, propanol, butanol, etc.), acetic acid, acetates, hydrogen, etc. Various strains of acetogens have been described for use in the production of liquid fuels from syngas: Butyribacterium methylotrophicum, Clostridium autoethanogenum, Clostridium carboxidivorans, Clostridium ljungdahlii, Clostridium ragsdalei. 
U.S. Pat. No. 5,173,429 to Gaddy et al. discloses Clostridium ljungdahlii ATCC No. 49587, an anaerobic microorganism that produces ethanol and acetate from synthesis gas. U.S. Pat. No. 5,807,722 to Gaddy et al. discloses a method and apparatus for converting waste gases into useful products such as organic acids and alcohols using anaerobic bacteria, such as Clostridium ljungdahlii ATCC No. 55380. U.S. Pat. No. 6,136,577 to Gaddy et al. discloses a method and apparatus for converting waste gases into useful products such as organic acids and alcohols (particularly ethanol) using anaerobic bacteria, such as Clostridium ljungdahlii ATCC Nos. 55988 and 55989. U.S. Pat. No. 6,136,577 to Gaddy et al. discloses a method and apparatus for converting waste gases into useful products such as organic acids and alcohols (particularly acetic acid) using anaerobic strains of Clostridium ljungdahlii. U.S. Pat. No. 6,753,170 to Gaddy et al. discloses an anaerobic microbial fermentation process for the production of acetic acid. U.S. Pat. No. 7,285,402 to Gaddy et al. discloses an anaerobic microbial fermentation process for the production of alcohol.
US Patent Application No. 20070275447 discloses a clostridia bacterial species (Clostridium carboxidivorans, ATCC BAA-624, “P7”) that is capable of synthesizing, from waste gases, products which are useful as biofuel. US Pat. Appl. No. 20080057554 discloses a clostridia bacterial species (Clostridium ragsdalei, ATCC BAA-622, “P11”) that is capable of synthesizing, from waste gases, products which are useful as biofuel.
WO 2007/117157 discloses methods of anaerobic fermentation processes that produce acetate as a by-product in addition to a desired product, and that can utilize hydrogen and/or carbon dioxide in the fermentation. In this disclosure fermentation is carried out by one or more strains of bacteria selected from Clostridium, Moorella and Carboxydothermus. WO 2009/064200 discloses a class of bacteria which has improved efficiency in the production of ethanol by anaerobic fermentation of substrates containing carbon monoxide. As disclosed, the exemplified bacterium, Clostridium autoethanogenum, is capable of producing ethanol and acetate.
Syngas can be converted to various chemicals and fuels using chemical catalytic routes such as process using catalysts containing Cu & Zn to make methanol or mixed alcohols, process using catalysts containing Co & Rh to produce ethanol and Fischer-Tropsch type synthesis to make olefins, etc. WO 2009/035851 discloses methods of converting syngas into ethanol and/or other higher alcohols using reactors comprising catalyst capable of converting syngas to alcohols said catalyst comprising at least one Group IB element, at least one Group IIB element, and at least one Group IIIA element.
WO 2010/002618 discloses a method for making alcohols from a gas comprising hydrogen and carbon monoxide comprising: passing the gas through a reactor containing a carried catalyst comprising elemental molybdenum, cobalt and an alkali or alkaline earth metal, and/or hydrides thereof.
Production of chemicals or power in general depends upon the quality of syngas produced, e.g. amount or concentration of CO and H2 in syngas as well as the ratio of CO/H2. Methods known for increasing ethanol yield by improving concentration CO and H2 in syngas as well as the ratio of CO/H2 include co-gasification of carbon dioxide, methane-containing gas such as landfill gas with carbonaceous material in the gasifier. WO 2009/154788 discloses a method of synthesis gas production via gasification of carbonaceous material in a gasifier comprising: injecting carbon dioxide gas, oxygen gas, and carbonaceous material into a gasifier; creating syngas comprising carbon monoxide and hydrogen.
WO 2009/112334 discloses a process wherein there is fed to the gasification step of gasifiable feedstock landfill gas which is mixture of predominantly methane, carbon dioxide and hydrogen sulfide obtained at a landfill site.
Thus U.S. Pat. No. 6,595,001 disclose a method of utilizing a methane-containing gas by feeding the methane-containing gas to a gas engine/generator assembly.
A widely used process of gasification of carbonaceous materials to produce syngas rich in CO and H2 uses an oxygen-deficient or oxygen-starved atmosphere in the gasifier that prevents complete conversion of carbon in the carbonaceous material. However, under oxygen-starved condition part of the carbon content of the carbonaceous materials often remains as un-reacted carbon particles or soot in the product syngas. Another part of the carbon content of the carbonaceous materials remains as un-reacted carbon in ash.
Incomplete conversion of carbonaceous feedstock to CO and H2 means less available CO and H2 for production of power or chemicals (e.g. ethanol). Increased amount of un-reacted or unconverted carbon particles or soot in the raw syngas increases difficulty and cost of cleaning up syngas. Increased amount of un-reacted carbon in ash increases difficulty and cost of disposal of ash.
It would be desirable to have a method of operation of gasifier that maximizes production of power or chemicals from the syngas produced from gasifier while keeping amount of un-reacted or unconverted carbon particles or soot in the raw syngas and amount of un-reacted carbon in ash under desirable low values especially when a methane-containing gas is co-gasified with carbonaceous material feed.
The present disclosure provides various new and desirable gasifier designs and methods of operating a gasifier that are not known in the art. The present disclosure accomplishes the needs described above.